/*
https://leetcode.cn/problems/climbing-stairs/
力扣70.爬楼梯
*/
class Solution {
public:
    int climbStairs(int n) {
        int p=0,q=0,r=1;
        for(int i=1;i<=n;++i){
            p=q;
            q=r;
            r=p+q;
        }
        return r;
    }
};